The use of adhesives and sealants in the automotive industries is becoming increasingly important. Adhesives and sealants are used in the assemblies of such hem-flanged parts as doors, decks and hoods. For example, sealing materials can be used in conjunction with more conventional spot-welding techniques. The sealant is first applied and then the sheet metal is welded through the sealant. Such a combined approach has allowed the distance between spot welds to be increased while reducing the number of welds. Some manufacturers, moreover, have eliminated the welding altogether by employing structural adhesives.
However, the use of adhesives has presented several distinct disadvantages. Unless carefully applied, the use of adhesives and sealants can be a messy operation requiring manual cleanup. If too much adhesive is applied or if it is not properly covered in the hemming operation, it can contaminate the electrophoretically deposited paint primer baths that are necessary prior to painting. Additionally, excess adhesive can also contaminate hemming dies. The flanges and method for joining parts must be structured to avoid wiping the adhesive from the part once the adhesive is applied thereto. It is not possible to paint over some adhesives and sealants, amplifying the need for accurate dispensing of these materials onto the specific component piece.
Heretofore, the manual application of adhesives and sealants to assemblies has been found to be generally impractical because of the high throughput and high accuracy required. As a result, the present automotive manufacturing environment places exacting demands on systems that can automatically apply adhesives and sealants.
Adhesives and sealants must be applied accurately, along the right bead path, in the required cycle time, in the precise volume required, and with the proper cross section. Otherwise, incorrect bonding or squeezing or bead placement will occur.
A dispensing system must be designed to handle the throughput requirements of the production assembly line as well as the geometry of the workpiece. Cycle times can be as short as 3 to 4 seconds for dispensing material around the entire perimeter of a door. At constant dispensing-head velocity, an adhesive or sealant must be delivered at constant pressure and flow to produce a uniform bead.
It has been found that a robotic dispensing system can generally accommodate the aforementioned requirements and substantially alleviate the above-enumerated disadvantages of adhesive use. However, significant limitations are still found in the actual adhesive dispensing system.
It is therefore an object of this invention to provide an orbiting nozzle dispersion apparatus for the application of a pattern of adhesive material or the like. The material flow rate is adjusted by varying the pressure supplied to the nozzle. The pattern width is varied by adjusting the distance between the nozzle and the work surface. Moreover, there is substantially no change in pattern width due to pressure variations in the material flow while the nozzle is maintained within a predetermined range of the work surface.